The desirable characteristics of an electrochemical gas generator for a fluid dispenser are:
I. The generator should be compact, eg. with a volume less than about 10% of the fluid to be dispensed, and be capable of delivering a total volume of gas (at STP) several times (eg. 4 times) the total volume of the dispensed fluid. PA1 II. The gas production should be switchable (on/off). PA1 III. The rate of gas generation should be controllable over a wide (eg. tenfold) range. PA1 IV. The rate of gas generation should be relatively unaffected by changes in temperature. For this purpose the electronic circuit connecting the poles of the reactor may beneficially include a high resistance with a positive coefficient of resistivity, so that as temperature is increased the drop in electrolytic resistance is compensated by a corresponding increase in electronic resistance. PA1 V. Once switched on the gas generation should be spontaneous, without requiring an external source of power. PA1 VI. The unit should have a long "shelf life" (eg. one year) and should not generate gas when not switched on (ie. no self discharge). PA1 (a) Fluid dispensers as described and claimed by Graf in U.S. Pat. No. 5,547,043 and Satzinger and others. These dispensers are driven by gas, usually hydrogen, which is produced by the spontaneous reaction of a short circuited bimetal galvanic couple, for example zinc/molybdenum, with an aqueous electrolyte, for example aqueous potassium hydroxide. PA1 (b) Fluid dispensers as described and claimed by Orlitzky et al in U.S. Pat. No. 4,023,648 and Winsel in Canadian Patent 1,333,579. These dispensers are driven by a gas, usually hydrogen, produced by spontaneous reaction of metal electrodes, for example zinc/hydrogen on nickel, in a monopolar electrochemical cell with the electrodes connected and controlled through an external electronic resistance. PA1 (c) Fluid dispensers, as described by Orlitzky et al in the above U.S. Pat. No. 4,023,648 and Yang in U.S. Pat. No. 5,404,966. These dispensers are driven by gas, for example nitrogen, produced by a monopolar electrochemical cell driven by a separate battery, connected and controlled through an external electronic resistance. PA1 (d) Bipolar electrochemical hydrogen generators, such as described and claimed by Fidelman in U.S. Pat. No. 3,256,504 and Pacheco in U.S. Pat. No. 5,089,107. These generators have metal anodes, for example magnesium or aluminium, with inert cathodes connected in series with an external resistance and activated to spontaneously produce hydrogen when immersed in salt water. PA1 (e) Bipolar batteries, such as described and claimed by Bowker in U.S. Pat. No. 5,395,709 and Meadows in U.S. Pat. No. 5,527,642. In this equipment a plurality of spontaneous electrochemical cells contained in a housing is connected through bipolar walls to form a battery stack for energy generation. PA1 (f) Bipolar electrochemical reactors for hydrogen generation, for example as described by Oshima et al in U.S. Pat. No. 5,401,371. These reactors are used for the electrolysis of water to generate both hydrogen and oxygen and are driven by an external source of energy. PA1 an anode of a metal whose standard oxidation potential is above that of hydrogen in the same electrolyte; PA1 a solid electrolyte; PA1 a cathode comprising an inert electronic conductor with a surface in contact with said solid electrolyte, said surface being electrochemically catalytic for the formation of hydrogen.
Prior work in this field can be divided into five areas:
The above prior art fails to satisfy the desirable criteria set out above. For example (a) gives a compact spontaneous unit but it is not switchable. Also as it operates through an electronic short circuit it is relatively sensitive to change in temperature. The gas generators of (b) are switchable, spontaneous and controllable through an external electronic resistance. However the magnitude of the external resistance is limited by the relatively low voltage available from a monopolar electrochemical cell, for example about 0.4 volts from zinc/hydrogen. The systems of (c) are switchable and controllable through a large external resistance and so relatively insensitive to temperature. But they are not spontaneous and require external batteries for operation. For example two, 1.5 volt batteries in series may be required.
The bipolar electrochemical gas generators of (d) are spontaneous and it is claimed that they are controllable through an external resistance. However as shown in U.S. Pat. Nos. 3,256,504 and 5,089,107 these bipolar units are not switchable or controllable but will generate hydrogen spontaneously when in contact with an electrolyte, for example salt water. This is due to electronic short circuits between anodes and cathodes in a common electrolyte. The bipolar batteries described under (e) are spontaneous and may be assembled to deliver multiples of the unit cell voltage but batteries are not required to produce gas, in fact batteries are designed to avoid gas generation. Finally hydrogen generators such as described in (f) require an external power source and produce oxygen and hydrogen at the same time.